The present invention relates to a method and apparatus for generating On-Screen-Display (OSD) messages using a field doubling mode. More particularly, this invention relates to a method and apparatus that reduces the memory bandwidth requirements of a decoding/displaying system by repeating a top field of OSD data in the bottom field for an OSD region.
On-Screen-Display messages play an important role in consumer electronics products by providing users with interactive information such as menus to guide them through the usage and configuration of the product. Other important features of OSD include the ability to provide Closed Captioning and the display of channel logos.
However, the heightened standard of digital video technology presents an ever increasing problem of generating and displaying OSD messages. For example, there are specific High Definition Television (HDTV) requirements that an HDTV must display up to 216 characters in four (4) xe2x80x9cwindowsxe2x80x9d versus the current National Television Systems Committee (NTSC) requirements of a maximum of 128 characters in one xe2x80x9cwindowxe2x80x9d. These new requirements place severe strains on the decoding/displaying system used to decode and display television signals (e.g., HDTV, NTSC, MPEG, and the like), which must decode the incoming encoded data streams and present the decoded data to a display system with minimal delays. Since OSD messages must be displayed (overlaid) with the video data, the microprocessor of the decoding/displaying system must assign a portion of the memory bandwidth to perform OSD functions, thereby increasing the memory bandwidth requirements of a decoding/displaying system and the overall computational overhead.
WO 90/15502 discloses a method and apparatus for superimposing information upon video signals and the like. Data which is to be combined with a composite video signal is stored in a replaceable memory device. A composite (e.g. television) signal is provided to an input. Horizontal and vertical sync signals are separated at a separator and then used to synchronize the reading functions from memory. In addition to display information, the data stored in memory includes frame count, line count and positional information by which initiation, line location and within-line position, respectively, of the display information are determined. The display information may include subliminal, supraliminal or both; and may be displayed repeatedly. A similar technique is employed to combine sound data with audio signals.
Thus, a need exists for a method and apparatus for generating On-Screen-Display (OSD) messages without increasing the hardware requirements, e.g., memory bandwidth, of a decoding/displaying system.
The invention concerns an apparatus and concomitant method for generating OSD messages by constructing a valid OSD bitstream with instructions in the OSD header to repeat a top field of OSD data in the bottom field for an OSD region.
More specifically, in accordance with the invention, an OSD unit retrieves an OSD bitstream from a storage device. The OSD bitstream contains an OSD header and OSD data. The OSD header contains control information that is used to program a color palette of the OSD unit and to provide instructions as to the treatment of the OSD data. The control information is programmed by a processor of a decoding/displaying system.
The control information includes two OSD pixel data pointers, an xe2x80x9cOSD Top Block Pointerxe2x80x9d and an xe2x80x9cOSD Bottom Block Pointerxe2x80x9d. These pointers (flags) inform the OSD unit where the top and bottom OSD pixel data are located respectively in the memory. By setting both pointers to the same value, the OSD unit repeats an OSD line of pixels in the other field. Namely, the top and bottom fields share the same OSD data.